As is well known, a welding fluid usually comprises a mixture of gases. The gases concerned are argon (Ar), helium (He), oxygen (O.sub.2) and carbon dioxide (CO.sub.2), the relative mixtures being binary or ternary, for example the mixtures can be:
a) Ar--CO.sub.2 ; PA1 b) Ar--CO.sub.2 --O.sub.2 ; PA1 c) Ar--He; PA1 d) Ar--He--CO.sub.2.
These gases are supplied to that region of an article at which the weld is to be made usually already mixed together.
It is known to use cylinders containing the mixture which are directly conveyed to the site at which the weld is to be made. This operation can however create safety problems in the workplace.
A system involving the preparation of welding mixtures on site is used where such mixtures are consumed in large quantity, it then being economically and logistically justified to use liquefied gas storage (Ar and/or CO.sub.2).
It is also know to prepare such welding mixtures in which the components Ar and CO.sub.2 are stored in the liquid phase (for example in large cryogenic tanks or cold evaporators) and the other components are stored in respective cylinders. The various components are mixed in known manner to obtain the final welding mixture. This known method (and relative plant) does not however ensure a mixture with constant composition characteristics. This negatively affects the execution of the weld, with the result that this latter often does not satisfy the severe codes which generally govern welding operations.